Control



Nov. 21, 1933. M. LOTHROP CONTROL 7 Filed April 24, 1951 2 Sheets$heet l INVENTOR. Marcus [of/Wop A TTORNEYS.

Nov.- 21, 1933.

M. LQTHROP CONTROL Filed April 24, 1951- 2 Sheets-Sheet 2 IN V EN TOR. Marcy; [of/Mop A TTORNEYS.

Patented Nov. 21, 1933 UNITED STATES PATENT OFFICE 30 Claims.

My invention relates to means for generating vapor and particularly to the control of steam generators of the forced circulation type such as have come into use for automotive purposes, particularly in the propulsion of automobiles. Such a generator or boiler usually comprises a relatively long tube which is subjected to heat and into one end of which feed fluid is introduced and from the opposite end of which the resulting l0 vapor or steam is released. Although such generators are advantageous for numerous reasons they present many difllcult problems. In automotive installations the load on the boiler fluctuates rapidly and widely. That is, the steam demand may be practically negligible at one moment and may be the full capacity of the boiler at the next moment with all gradations between the maximum limits following each other without any particular order or periodicity. It is considered important in such generators that the steam or other vapor be supplied at substantially a constant temperature and that the pressure fluctuations have little or no effect on the temperature of the vapor. It is likewise customary to relate the pressure and temperature so that the vapor issuing from the generator is superheated.-

Since generators of the forced circulation type require that the feed fluid introduced into the inlet end of the boiler tube must traverse the entire length of the tube before emerging as vapor, any change in the amount of feed fluid introduced is relatively slow in afiecting any controlling devices situated adjacent the outlet end of the tube. In one practical installation the length of the boiler tube is approximately 600 feet and the length of time elapsing between the introduction of feed. fluid and its discharge as vapor from the outlet end is of the order of one minute. This delay or time lag is much too great for a satisfactory and quickly responsive control system.

An object of my invention is to provide a con trol in which the temperature of the vapor issuing from the vapor generator is maintained at substantially a constant value.

Another object of my invention is to provide a control which is quickly responsive.

The foregoing and other objects are attained in the embodiment of the invention shown in the drawings, in which Figure 1 is a schematic diagram of a control in accordance with my invention.

Figure 2 is a schematic diagram of a modified form of control in accordance with my invention.

In its preferred form, the control of my invention comprises a relatively long heated tube having an inlet into which feed liquid is introduced and having an outlet adjacent which a thermostat is located, together with a conduit for conducting fluid from the evaporation zone of said tube back into said tube adjacent said thermostat, for controlling the introduction of feed liquid into said tube.

In the form of my invention disclosed in Figure 1 there is' provided a vapor generator or boiler of the forced circulation type. The boiler comprises a casing 6 within which is situated a relatively long boiler tube 7 coiled into tortuous convolutions and having an inlet 8 and an outlet 9. In order to heat the tube 7, there is preferably provided a blower 11 driven by an electric motor 12 or other suitable means for inducing a current of air to flow through a venturi 13 and discharge into the combustion space 14 of the boiler casing 6. To carburet the air a carburetor 1 6 of any convenient kind intersects the venturi 13. The resulting fuel air mixture is preferably ignited by a standard spark plug 17 situated near the discharge of the venturi 13. Products of combustion from the combustion space 14 flow over the ,convolutions of the tube 7 releasing their heat thereto and discharge from the boiler casing 6 through a flue 19.

I preferably provide a source of feed fluid or liquid such as a water tank 21 and introduce liquid from the tank 21 into the boiler tube by means of a pump 22. The pump withdraws liquid from the tank 21 through a conduit 23 and discharges the liquid through a conduit 24 into the inlet 8 of the tube 7. A check valve 26 prevents back flow from the boiler into the conduit 24.

The feed liquid introduced into the inlet 8 of the boiler tube progresses through the tortuous tube toward the outlet 9 thereof and as it advances through the tube gradually becomes heated. The

liquid adjacent the foot of the boiler, generally designated A, is at a relatively low temperature which gradually increases as the liquid flows through the convolutions until the liquid absorbs suflicient heat to be converted gradually into vapor or, in other words, to change its state. Under steady conditions of operation the liquid changes into vapor at a relatively definite point in the length of the tube '7, but due to fluctuating pressures in the boiler tube '7, due to fluctuations in the amount of heat imparted to the tube, and due to other causes the point at which the last drop of liquid in the mixture of liquid and vapor ess is evaporated into vapor travels back and forth the tube 7 within relatively wide limits but n vertheless within a certain region of the boiler, ndicated by the letter B. There is, therefore, no such thing as water level" in a forced circulatlon boiler, but the region B can with accuracy be termed an evaporating region or zone. Vaper which continues to travel from the region 35 of the boiler tube through the remaining convolutions becomes superheated and can be discharged from the boiler tube 7 under the control of a throttle valve 27.

In order to regulate or control the operation of the supply of heat to the tube 7 and the supply of feed fluid thereto, I preferably interpose in the tube 7 between the inlet 8 and the outlet 9 thereof a thermostat 28. The thermostat is preferably located, with respect to the length of the tube, relatively near the outlet 9 thereof and in thermal relation to the tube itself. The thermostat includes a rod 29 which projects from the boiler casing and moves in accordance with temperature variations of the boiler tube 7. If desired, the thermostat can be responsive to other boiler conditions than tube temperature, such for instance, as steam temperature, the temperature of the products of combustion and so forth.

The rod 29 is preferably connected to a rocker 31 having resilient arms 32 and 33. Mounted on the resilient arms 32 and 33 are contacts 34 and 36, respectively, which are connected by flexible leads 38 and 39 to a conductor 41 extending to a contact 42. Cooperating with the contact 42 is a similar contact 43 carried at the extremity of a lever 44 which is actuated by a pressure responsive cell 46. This device 46 is in communication by a pipe 47 with the outlet 9 of the boiler tube 7, so that when the pressure within the boiler tube exceeds a predetermined value the cell 46 causes the lever 44 to separate the contact 43 from the contact 42 and provide an interruption in the circuit. The contact 43 is connected preferably by a lead 48 to a master switch 49 controlling the circuit from a storage battery 51 or other suitable source of electrometive force. One side of the battery 51 is preferably grounded as at 52.

When the pressure within the boiler tube 7 is below the predetermined value and the master switch 49 is closed the contacts 34 and 36 are provided with current. When the temperature of the boiler tube 7 is relatively low or is below a predetermined value the contact 36 is in abutment with a cooperating contact 56, as indicated in Figure 1, and electricity flows through a wire 57 to one side of the electric motor 12 the other side of which is connected to ground by a lead 58. Likewise connected in circuit with the electric motor 12 is an induction coil 59 for energizing the spark plug 17. Thus, up to a predetermined temperature of the boiler tube 7 the electric motor 12 is energized and the blower 12 is effective to supply the combustion chamber 14 with a combustible mixture which, when burning, imparts heat to the boiler tube 7.

As the temperature of the boiler tube 7 increases, the thermostat rod 29 gradually moves the rocker 31 until at a predetermined tempera: ture the contact 34 abuts a cooperating contact 61. The contact 61 is connected by a wire 62 to one side of an electromagnet 63 or solenoid the other side of which is connected to ground by a lead 64. The solenoid 63 controls operation of a valve 66 which regulates communication through a conduit 67 extending from the outlet psi 9 of the boiler tube 7 to a steam engine 68 for operating the feed fluid pump 22. When the contacts 34 and 61 abut at their predetermined temperature, which preferably is a temperature somewhat lower than the temperature at which the contacts 36 and 56 are separated, current fiows through the conductor 62 to energize the solenoid 63 so that the valve 66 is opened and steam or other vapor from the boiler tube outlet 9 operates the engine 68 and causes the pump 22 to withdraw feed fluid from the tank or reservoir 21 and introduce it into the foot A of the boiler tube 7.

Due to the long interval of time necessary for feed fluid introduced into the foot A of the boiler tube to reach and act upon the thermostat 28, which is located at the region of the boiler, generally designated C in Figure 1, I have found that a control system constructed as so far described is relatively unsatisfactory andinefiective for the result desired.

In accordance with my invention, therefore, '1 preferably connect a conduit 71 from the region B of the boiler tube 7 to the region C thereof, that is, the conduit 71 shunts a portion of the tortuous boiler tube 7 between the inlet 8 and the oulet 9 thereof and provides a much shorter path for fiuid from the region B to a point just in advance of the thermostat 28, or at the region C. The conduit 71 preferably diverges tangentially from an abrupt bend in the tube 7, so that a liquid and vapor separating action occurs. With the conduit 71 establishing a short circuit or short path from the end point of the water or liquid in the tube 7 to the thermostat 28 the thermostat is then quickly responsive to the state of the fluid within the boiler tube 7 adjacent the region B.

When feed liquid is introduced into the inlet 8 and progresses through the tube if, when it arrives at the region B, it is still in the liquid state, some of such liquid flows through the shunting conduit 71 and discharges back into the tube 7 immediately in advance of the thermostat 28 and cools the thermostat appreciably. This effect is pronounced since the water or other liquid has a relatively large heat absorbing capacity as contrasted to the small heat absorbing capacity of vapor and absorbs a great deal of heat from the thermostat 28, thus reducing its temperature quickly. If, on the other hand, the feed liquid forced into the foot 8 of the tube 7 has evoporated into steam or has changed its state and become vapor prior to the time it reaches the region B, then a part of such vapor flows through the shunting conduit 71 and being re-introduced into the tube 7 adjacent the thermostat 28 has relatively little or no eifect thereupon to reduce the temperature inasmuch as the heat absorptive properties of vapor are relatively insignificant in comparison with the heat absorptive properties of liquid. In the latter event the temperature of the thermostat 28 is not prevented from reaching is predetermined value at which the contacts 34 and 61 are brought into abutment. The pump 22 introduces feed liquid into the inlet 8 of the boiler tube 7 until such time as liquid arrives at the region B and a portion thereof is discharged through the shunting conduit '71 onto the thermostat whereupon a reduction in the temperature of the thermostat causes the contacts 34 and 61 to separate and diminish or stop the operation of the feed fluid pump 22.

By virtue of the control disclosed in Figure 1 the temperature of the steam issuing through the throttle valve 27 is substantially at a predetermined value and is approximately constant despite fluctuations in load upon the boiler or in the pressure of the issuing vapor.

In many systems for controlling forced circulation vapor generators such as boilers, the operation of the control, although generally quite satisfactory, is relatively erratic and has numerous vagaries from the time the boiler is started from cold until it has been operated for a suflicient period to permit conditons to become approximately constant. One of the diiflculties encountered is that when a forced circulation boiler is shut down after running and the steam contained therein condenses, feed fluid is induced to flow into the boiler tube by virtue of the vacuum existing therein so that when the boiler is again placed into operation an excessive amount of feed liquid is contained therein without means of escape. Furthermore, in a forced circulation boiler having a relatively long tube, it is possible for portions of the tube, in bringing the boiler up to operating condition from cold, to become locally overheated because there is no circulation or flow of fluid through the tube until such time as the feed fluid pumps are operated. To overcome these difliculties as well as numerous others I have disclosed in Figure 2 a modification of the control of my invention shown in Figure 1, the general arrangement being identical but certain changes being incorporated in the electrical circuit so that the pressure of the vapor operates in conjunction with the temperature of the boiler tube to control the feed fluid pump.

In the form of my control shown in Figure 2, a boiler casing 106 is provided and is supplied with heat by acombustible mixture emanating from a venturi 107 intersecting the boiler casing and supplied with a current of carburetted air from a blower 108 and a carburetor 109. The blower 108 is operated by an electric motor 111 or any other suitable driving means and the current of combustible mixture is ignited by a standard spark plug 112.

To absorb the heat from the combustible mixture burned within the casing 106 I preferably provide a relatively long tortuous boiler tube 113 which has an inlet 114 and an outlet 116. A pump 117 driven by a steam engine 118 withdraws feed liquid from a reservoir 119 through a conduit 121 and discharges through a conduit 122 leading to the inlet 114 and under control of a check valve 123 to prevent back flow.

To supply the steam engine 118 with operating vapor a conduit 126 extends to the outlet 116 of the boiler just in advance of a throttle valve 127 controlling the efflux of generated vapor therefrom. For controlling communication through the conduit 126 and therefore controlling the operation of the pump 117 and the introduction of feed fluid into the inlet 114, I preferably situate a valve 128 in the conduit 126 and operate the valve electromagnetically by means of a solenoid 129. Located proximate the outlet 116 and in thermal relation with the boiler tube is a thermostat 131 having a rod 132 projecting from the boiler casing 106 and moving in response to changes in temperature of the tube 113, although variations in other boiler conditions can be utilized to operate the rod 132. Preferably, in order to make thermostat 131 responsive to the state of the fluid flowing through the tube 113 in the region 13 thereof, I provide a shunting conduit 133 intersecting the tube 113 adjacent the region B and re-entering the tube 113 at the region generally designated C immediately in advance of the thermostat 131.

To make the movement of the thermostat rod 132 efiective upon the means for supplying heat and the means for supplying feed fluid, I connect the rod 132 to a rocker 136 having flexible arms 137 and 138. The flexible arm 138 is provided at its extremity with an electrical contact 139 cooperating with a contact 141. The contact 141 is joined by a lead 142 to one side of the electric motor 111, the other side of which is connected to ground by a conductor 143. An induction coil 144 in circuit with the conductor 143 affords energization for the spark plug 112 concurrently with the energi'zation of the electric motor 111. For supplying current to the contact 139 a flexible lead 146 joins the contact to a conductor 147 extending to a contact 148. Carrying the contact 148 is one arm 149 of a bell crank, generally designated 151, which is joined to move with a pressure responsive device 152 connected by a duct 153 to the conduit 126 and which is therefore responsive to pressure withinthe tube 118 adjacent the outlet 116 thereof. In accordance with this arrangement, the bell crank 151 is moved in accordance with the pressure existing adjacent the outlet 116 of the boiler tube and moves the contact 148 accordingly.

Adapted to abut the contact 148 is a cooperating contact 156 carried at the extremity of the flexible arm 157. In the path of the arm 157 is a fixed or adjustable stop 158 for limiting the movement of the contact 156. The contact 156 is connected by a wire 159 to a storage battery 161 or other suitable source of electromotive force through a master switch 162. Preferably, one side of the storage battery 161 is connected to ground by a lead 163. The contacts 148 and 156 are in abutment and permit current to flow from the wire 159 into conductor 147 until such time as the pressure adjacent the outlet 116 of the boiler tube arrives at a predetermined value, above which the contact 148 is moved away from the contact 156 since at the predetermined value the arm 157 abuts the stop 158. When the contacts 148 and 156 are closed current flows likewise through the contacts 139 and 141 which are in abutment when the temperature of the boiler tube is below a predetermined value and causes the electric motor 111 to be energized and the spark plug 112 to ignite the combustible mixture and supply heat to the boiler tube 113. When the temperature of the thermostat 131 increases to a predetermined value the contacts 139 and 141 are separated thus breaking the circuit to the electric motor 111 and the spark plug 112 and interrupting the supply of heat to the boiler tube 113.

In order to control the operation of the steam engine 118 operating the pump 117, the arm 137 of the rocker 136 is preferably provided with a contact 171 connected by a flexible lead 172 to the conductor 147. Cooperating withthe contact 171 is a contact 173 mounted at the extremity of a flexible arm 174 forming part of the bell crank 151 and under the control of the pressure responsive device 152. A fixed or adjustable stopthe contacts 171 and 173 are in abutment and the valve 128 is therefore opened and the feed fluid pump 117 is eiiective to introduce feed fluid into the boiler tube 113. The contacts 171 and 1'13 may remain closed and move in unison under the influence of the thermostat 131 and the pressure responsive device 152 until such time as the flexihis arm 174 abuts the stop 1'76 and if the contacts 171 and 173 stay in abutment during this time the pumps operate continuously. Ii, however, during such movement of the thermostat rod 132 and of the bell crank 151 the pressure should increase faster than the temperature, then the contact 173 is separated from the contact 171 and the valve 128 is closed, thereby interrupting operation of the feed fluid pump 117. The arrangement and proportions of the bell crank 151 and of the rocker 13b can be such, if desired, that the pump will operate at any time when the boiler pressure is below a corresponding boiler temperature and will not operate when the boiler pressure exceeds a corresponding boiler temperature, with the ratio between the boiler pressure and boiler temperature being any value desired.

After the boiler pressure has increased sufi'iciently to cause the arm 1% to abut the stop 176 any further increase in pressure above this predetermined value causes the contact 148 to leave the contact 156 and interrupt the operation of the pump 11'! and of the blower 108. The adjustment is usually such, however, that prior to interruption of the operation by the contacts 148 and 156, the increase in temperature is such as to cause the contacts 139 and 141 to separate thereby interrupting the operation of the heat supplying means alone without affecting the operation of the pump 117.

In accordance with the control as disclosed in Figure 2, when the boiler is cold and the master switch 162 is closed the temperature usually increases much faster than the pressure so that the contacts 1'71 and 173 are promptly in abutment causing the steam engine 118 to operate and the pumps 117 to introduce feed fluid into the boiler. The operation of the steam engine 118 provides an outlet for the fluid contents of the tube 113 and causes a circulation or flow therethrough to prevent localized overheating oi the tube and likewise permits the discharge of excessive pres sure due to a superabundance of feed fluid having accumulated in the boiler tube because of the cold condition thereof. As however, as system has come up substantially to operating pressure and temperature as evidenced by the arms 157 and 1741 having contacted their respective stops 158 and 176, the control operates in the same fashion as the control disclosed in Figure 1.

It is to be understood that I do not limit myself to the form of the control shown and described herein, as the invention, as set forth in the following claims may be embodied in a plurality of forms.

I claim:

1. A control comprising a relatively long heated tube, means for introducing feed fluid into one end of said tube, and a conduit shunting an intermediate portion of said tube between the evaporating region and a point spaced from the discharge end of said tube.

2. A control comprising a relatively long tortuous tube, means for heating said tube, a thermostat in thermal relation to an intermediate portion of said tube, means for introducing feed fluid meager tube, means for heating said tube, means for introducing feed fluid into said inlet, and a conduit shunting said tube between the evaporating region of said tube and said thermostat.

i. A control comprising a-tube having an inlet and an outlet, means for heating said tube, means for introducing feed liquid into said inlet where by in one region of said tube said liquid is eon= verted into vapor, and a conduit for conducting fluid from said region into said tube adjacent said outlet.

5. A control comprising a relatively long tortuous tube having an inlet and an outlet, means for heating said tube, means for causing feed liquid to flow through said tube from said inlet toward said outlet whereby in one region of said tube said liquid is converted into vapor, and a conduit for conducting fiuid from said region into said tube adjacent said outlet.

6. A control comprising a heated tube having an inlet and an outlet, a pump for introducing feed fluid into said inlet, a thermostat proximate said outlet and in thermal relation to said tube for controlling said pump, and means for conducting some of said fluid from the evaporating region of said tube and reintroducing said fluid into said tube in advance of said thermostat.

'7. A control comprising a tube into one end of HG which feed fluid is forced and from the other end of which vapor issues; means for heating said tube; a thermostat subject to vapor temperature adjacent the delivery end of said tube, said thermostat serving to control the operation of means 115 for supplying said feed fluid; a by-pass conduit arranged to withdraw a portion of the fluid from the evaporation region of said tube and arranged to re-enter said withdrawn fluid into said tube to be effective upon said thermostat.

8. A control comprising a heating tube into one end of which feed fluid is forced and from the other end of which vapor issues; means for imparting heat to said tube; means for forcing said fluid into said tube; a thermostat adjacent 125 the outlet end of said tube subject to vapor temperature; a icy-pass conduit arranged to with draw a portion of the fluid th evaporation region of said tube and to re-enter said portion into said tube to influence said thermostat.

9- A control comprising a feed fluid pump sup-=- plying feed fluid to an evaporating tube, said tube being subjected to heat, whereby said feed fluid is converted into vapor which is delivered from the outlet end of said evaporating tube; a by-pass tube in communication with the evaporation region of said evaporating tube for drawing off a portion of the fluid from said evaporating tube and re-entering such drawn-off portion into the evaporating tube at a point not far from its delivery end; and a thermostat subject to steam temperature in said evaporating tube situated between the juncture of the delivery end of said bypass tube with said heating tube and the outlet end of said heating tube, said thermostat serving 145 to control the operation of said fluid pump.

10. A control comprising a feed fluid pump arranged to supply feed fluid to a heating coil, said coil comprising a long tube having an inlet end for feed fluid. and an outlet end for vapor; 150

a thermostat responsive to the temperature of said vapor and arranged to control the operation of said feed fluid pump; and a by-pass conduit for conveying a portion of the fluid from the evaporation region of said tube and returning said fluid to the portion of said tube in which said thermostat is located.

11. A control comprising a heated tube into the inlet end of which feed fluid is forced by a feed pump and from the outlet end of which vapor issues; a thermostat adjacent the outlet end of said tube and subject to vapor temperature, said thermostat controlling the operation of said feed pump; a duct for withdrawing a portion of the fluid from the evaporation region of said tube and returning said portion to said tube at such a point that said portion will have a prompt eflect on said thermostat.. v

12. A control comprising a tube, a burner for imparting heat to said tube, a feed fluid pump for forcing feed fluid into the inlet end of said tube; a thermostat responsive to vapor temperature adjacent the outlet end of said tube, said thermostat serving to control said feed fluid pump; a duct arranged to'withdraw a portion of fluid from the evaporation region of said tube and re-entering said withdrawn fluid into said tube to be effective upon said.thermostat.

13. A control comprising a tube, a feed fluid pump for supplying said tube with feed fluid, a burner for heating said tube, a thermostat subject to vapor temperature adjacent the outlet end of said tube, said thermostats'erving to control the operation of said pump, and also serving to control the operation of said burner; and a bypass duct for conveying fluid and/or vapor from the evaporation region of said tube to. the portion of said tube just beyond which said thermostat is situated.

14. A control for a boiler system in which there is an extended boiler tube having an evaporation region comprising means for forcing feed fluid to traverse said boiler tube; a thermostat for controlling said means, said thermostat being responsive to the fluid temperature in said boiler tube, such fluid temperature being the resultant of the mixture of two portions of fluid, one of which has traversed the major portion ofthe boiler tube, and the other portion of which has traversed said portion of the boiler tube with the exception of that part of said boiler between the evaporation region thereof and said thermostat.

15. A control comprising a heating tube, a burner for imparting heat to saidtube, a feed pump for supplying feed fluid to said tube, a thermostat for controlling said feed pump and said burner, said thermostat being subject to the resultant temperature of the mixture of-two portions of the fluid within saidtube, one portion of which has traversed the major portion of said tube, and the other portion of which has traversed said portion of said tube with the exception 0; that part of said tube between the evaporation region thereof and said thermostat.

16. A control comprising a heating tube, a burner for imparting heat to said tube, a feed pump for supplying feed fluid to said tube, a thermostat adjacent the outlet end of said tube and serving to control said pump and said burner; a by-pass duct connected with said tube which allows a portion of the fluid within said tube to by-pass the portion of said tube between the evaporation region thereof and said thermostat.

17. A control comprising a tube having an inlet and an outlet, a thermostat in thermal relation to said tube proximate said outlet, a conduit shunting said tube between the evaporation region thereof and said thermostat, means under control of said thermostat for heating said tube, and means under control of said thermostat for introducing feed fluid intosaid inlet.

18. A control comprising a relatively long heated tube having an inlet and an outlet, means for forcing feed fluid into said inlet, a thermostat adjacent said outlet and an unheated conduit shunting said tube between the evaporation region thereof and said thermostat.

19. A control comprising a relatively long heated tube having an inlet and an outlet, a thermostat adjacent said outlet, a conduit shunting said tube between the evaporation region thereof and said thermostat, and means for forcing feed fluid through said tube, a majorportion traversing the entire tube and a minor portion traversing said conduit.

20. A control comprising a relatively long tube, means for heating said tube, means for introducing feed fluid into said tube to produce vapor; and means responsive to variations in the ratio of pressure of said vapor to temperature of said vapor from a predetermined ratio for controlling said introducing means.

21. A control comprising a long boiler tube,

means for heating said tube, means for introducing feed fluid into said tube, means responsive to pressure in said tube for rendering said introducing means inoperative, and means for varying in accordance with temperature in said tube the pressure at which said responsive means responds.

22. A control comprising a long boiler tube, means for'heating said tube, means for introducing feed fluid into said tube, and means for operating said introducing means only when the ratio of pressure in said tube to temperature in said tube is below a predetermined ratio.

23. A control comprising a long boiler tube adapted to contain fluid having characteristics of pressure and temperature, and means for introducing feed fluid into said tube only when the ratio of said pressure to said temperature is less than a predetermined ratio.

24. A control for a relatively long boiler tube in which there is an evaporating region, the control' comprising a controlling device operatively related to said tube, and a conduit shunting an intermediate portion of said tube for conducting fluid from said evaporating region directly to said device.

25. A control comprising a relatively long boiler tube having an initial portion, an intermediate portion and a final portion, there being an evaporating region adjacent the junction of said initial portion and said intermediate portion; a controlling device operatively related to said tube adjacent the junction of said intermediate portion and said flnal portion; and means for causing fluid in said evaporating region to be promptly effective on said controlling device.

26. The combination with a long heated tube having an evaporating region and a superheating region of means for introducing fluid into one end of said tube, and means for controlling the characteristics of the fluid discharging from said tube by variations in the temperature of fluid shunted directly fromsaid evaporating re- 1 gion.

271 The combination with a long heated tube into one end of which feed fluid is introduced and from the other end of which steam is dis= charged, of means for controlling the characteristics of the steam by variations in the temperature of a feed fluid mixture one component of which is feed fluid directly shunted between a plurality of thermally spaced zones in said tube one of which is the evaporating zone.

28. The combination with a long tuhe, of a casing enclosing said tube, means for introducing feed fluid into one end of said tube, means for introducing products of combustion into said casing whereby the tube is heated to progressively higher temperatures in the direction of flow of said fluid, and a device for controlling the characteristics of said fluid subjected to temperatures obtaining in a mixture of component portions of said feed fluid, each of said portions flowing directly from one of a plurality of thermally neeaeei spaced points in said tube one of said points being the evaporation point,

29. The combination with a heated tube hav ing an evaporation zone, of means for intro ducing feed fluid into one end of said tube, a control device associated with said tube, and means shunting an intermediate portion or" said tube to short circuit the path of the fluid from said evaporation zone directly to said control device.

34). The combination with a long heated tube having an evaporation zone and a superheater zone, of means for introducing fluid into one end of said tube, a control device thermally associated with the superheater zone, and means for conducting fluid directly from the evaporation zone to said control device.

MARCUS LOTHROP. 

